Chloroquine (CQ, 1) and hydroxychloroquine (HCQ) are known for their antimalarial activities and as inhibitors of autophagy in mammalian cells. However, their roles as anticancer agents are still emerging. Ferroquine (FQ, 2) and structurally-modified ferroquines have also been intensely studied as antimalarials. Ferroquine is mentioned as a possible antitumor agent in two recent papers (Reiter, C. et al. Eur. J. Med. Chem. 2014, 75, 403; Chellan, P. et al. Dalton Trans. 2014, 43, 513).

Despite their promise, a recent scientific report has suggested that the ionization constants (pKa) for CQ and HCQ are too high for them to be effective lysosomotropic agents in bulky tumors that create low pH environments in their interiors (Pellegrini, et al. Autophagy 2014 10, 1)